Finishing support racks usually have several, vertically stacked, horizontal rows or tiers of protruding, article-engaging hooks upon which workers hang workpieces for surface finishing. The hooks are connected to vertically spaced, horizontal crossbars which in turn are conventionally welded or bolted together at their opposite ends to vertical sidebars.
One workpiece supporting rack which is shown in the prior art is described in U.S. Pat. No. 4,097,359 and the patents referred to therein. Still another work holder is shown in U.S. Pat. No. 2,904,492.
The article engaging portion of the hooks may be constructed in a variety of shapes. Ordinarily each hook is simply a piece of wire having its article-engaging end bent into a hook shape. The term hook is utilized, however, to include the great variety of configurations which may be devised for engaging workpieces.
Finishing support racks are suspended from a conveyer and a large number of parts or workpieces are connected to the hooks of the rack. The rack and its suspended workpieces travel through a finishing system having a series of stations at which the workpieces may be sequentially treated by one or more of the steps of cleaning, rinsing, surface preparation such as undercoating, rinsing again, drying, coating and baking. Workers then remove the finished parts and reuse the racks.
Although the racks may be reused for more parts of the same type, eventually a particular job is completed and the rack may later be used for finishing other parts in connection with another job. However, each job is somewhat unique. Not only do parts vary in size from job to job, but they may come in different types of groupings of part sizes and configurations. For example, parts can be large or small, elongated, bulky or compact and additionally, where several parts for a particular assembly are finished together, some groups may have many small parts and a few large ones, other groups of parts may have many large and a few small parts and still other groups may have still a different variety or mixture of parts, sizes and shapes.
It is desirable that all parts which are to be finished be supported as closely together as possible consistent with permitting a quality finish to be obtained. By positioning the parts closer together on the rack, there is less empty or open area between the parts through which paint or coating material is sprayed and not coated on a part. Reduction of the open area reduces the need for expensive recycling of coating materials and the associated material loss in recycling processes. Furthermore, closer spacing permits more parts to pass through the finishing system on each rack thereby increasing the finishing rate and improving overall efficiency.
Prior art finishing support racks are conventionally welded or bolted together. Welding irrevocably commits the particular rack and the capital investment which is required to one unique size and spacing. The use of exposed bolts has the same effect because the bolts become coated and can not be unfastened thereby preventing disassembly of the rack. Although the rack may be excellent for one job it will be less efficient for most others. It is therefore an object of the present invention to provide a sturdy and durable support rack which the owner can purchase and thereafter change as he desires in order to space the hooks to efficiently accommodate each particular group of parts being finished for each job.
Still another object of the present invention is to provide a finishing support rack constructed of components which can be prefabricated and warehoused and later assembled as needed. The required components may be selected in accordance with a purchase order to form finishing support racks of a particular desired size. Not only may the support racks be shipped immediately because no further construction is necessary, but they may be shipped in a disassembled condition and therefore may be shipped in a very compact package which saves shipping expenses.
Additionally, it is an object of the invention to provide rack sidebars in a variety of sizes so that different sizes may be used to assemble and change the support rack with a different vertical crossbar spacing. A user need only stock a variety of relatively inexpensive sidebars at considerably less cost than stocking a variety of entire racks and yet can have the same variety of rack sizes available to him.
Finishing support racks are constantly recycled through the finishing system and become encrusted with multiple layers of coating material. In electrostatic painting, the coating particles are electrically charged and directed toward a suspended workpiece. The workpiece is electrically connected to the ground potential through the conductive support rack so that the coating material is attracted by a static electric field to the suspended workpieces. It is extremely important that the electrical contact between the sidebars and the crossbars and between each support hook and its crossbar be maintained as a good, low resistance electrical contact so that the suspended workpiece will remain well grounded. The accumulation of nonconductive or high resistance coating particles between these interconnected rack components must be prevented.
If the coating material is applied to the contacting, interfacing surfaces of these rack components it will create a high resistance in the circuit from ground to the workpiece which will inhibit electrical current flow. The current flow is necessary in order to supply electrons for neutralizing the charge of the coating particles after they are deposited on the suspended workpieces so that subsequently arriving, positively charged particles will be uniformly attracted to the workpieces. The undesirable electrical charge in the area of the workpieces being painted upon the support racks. The buildup of charge would reduce the attraction of the workpiece to the coating material causing uneven coating and creating a potential spark hazard.
A single painting or coating operation applies a coating layer to the exposed crossbars, sidebars and support hooks of the rack. This layer usually entirely covers the hooks except for the small area of direct contact with each suspended workpiece. Often a hook can be reused for an identical workpiece which will be in electrical contact with the hook at the identical place. However, for a workpiece which is positioned differently on the hook, even one layer of coating material reduces the electrical contact of the hook with the workpiece.
It is therefore desirable that the hooks of the support rack be detachably engaged to the main frame of the rack so that the hooks may be periodically removed, cleaned and replaced. Alternatively, they may be removed and replaced with new hooks or with ones of a different size or shape to accommodate different workpieces.
Another major difficulty with the prior art finishing support racks is the difficulty of removing the hooks from the main frame of the rack. Some require extensive manual manipulation while others require stripping and disassembly of the rack. Another disadvantage is that the prior art racks are more expensive to construct because they require more metal and more manufacturing operations than the rack of the present invention. Because of the manner that the hooks are attached to the main frame of prior art racks, they have a further disadvantage that the wire size used for the hooks of a particular prior art rack is narrowly limited to the particular wire size for which the rack was designed.
It is therefore another object of the present invention to provide a versatile finishing support rack which has hooks which are removable or replaceable with a minimum of human manipulation and with hooks of a broad range of wire sizes and yet provides a finishing support rack which is of a stronger and sturdier construction and easier to fabricate than prior art racks and still provides complete shielding of the electrical contacts between the hooks and the crossbars and between the crossbars and the sidebars of the support rack.